Device and method for removing rust on motor vehicle wheel brakes

ABSTRACT

A device for removing rust on a brake disk of a wheel brake includes a control unit which automatically activates a brake actuator in order to apply brake shoes to the brake disk of the brake if at least one vehicle parameter satisfies a predefined activation condition.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device for removing rust on motorvehicle wheel brakes.

2. Description of the Related Art

In most cases, electric and hybrid vehicles are braked by a generator inorder to be able to recover energy from the braking operation. On theother hand, the wheel brakes of a hydraulic brake system are used ratherrarely. This may cause rust to be deposited on the brake disks of thewheel brakes, which reduces the braking power.

To improve the braking power in wet conditions, the so-called brake diskwiping is known to be carried out. In this case, the brake shoes areapplied to the brake disks with light pressure, so that a water filmpresent on the brake disk is removed. The condition “wet” is normallydetected with the aid of a rain sensor. When this function is carriedout, rust is also in principle removed from the brake disk. However, thebrake disk wiping function for removing rust is only of limitedsuitability, since rust may also form on the brake disks when it doesnot rain for an extended time.

An object of the present invention is therefore to provide a device forremoving rust on the brake disks of a vehicle.

According to the present invention, a braking device having a rustremoval function is proposed which includes a control unit whichautomatically activates a wheel brake if at least one vehicle parametersatisfies a particular predefined activation condition. In contrast toenvironmental parameters, such as “wetness,” for example, all parametersaffecting the vehicle itself are understood to be vehicle parameters inthis case. Vehicle parameters according to the present invention are,for example: the vehicle speed, the engine torque of a vehicle engine,an ignition cycle counter content, time information such as, forexample, information concerning the operating time of the vehicle, or abrake pressure. If at least one of the vehicle parameters satisfies aparticular predefined activation condition, the rust removal functionaccording to the present invention is performed by applying the brakeshoes to the brake disks with a light brake pressure. This simplypolishes away the rust present on the brake disk. This invention is inparticular advantageous for electric and hybrid vehicles, since thehydraulic wheel brakes are used less often in these vehicles.

According to one preferred specific embodiment of the present invention,the engine torque of a vehicle engine is increased during the rustremoval in order to compensate at least partially for the braking effectof the rust removal. The engine torque of the vehicle engine may, forexample, be adjusted by the control unit. If the braking effect of thewheel brakes is completely compensated, the rust removal operation is nolonger noticeable for the driver.

According to one exemplary embodiment of the present invention, one ofthe vehicle parameters is an ignition cycle counter content, which maybe determined, for example, with the aid of a counter. In this case theassociated activation condition is, for example, satisfied if thepresently ascertained counter content is greater than the one in themost recently performed rust removal. In order to avoid unnecessarystresses of the brakes and save energy, the rust removal operationshould preferably be activated no oftener than once per ignition cycle.The rust removal function may be adjusted in such a way that it iscarried out only once each second, third or nth ignition cycle.

One of the vehicle parameters may also be a vehicle speed, which may bemeasured, for example, with the aid of wheel speed sensors. In thiscase, the associated activation condition is, for example, satisfied ifthe measured vehicle speed is higher than a determined threshold value.The threshold value may amount to, for example, 50 km/hr or it may alsobe lower, in the case of heavy vehicles, for example, 30 km/hr. This hasthe advantage that starting from a certain driving speed, the rustremoval is no longer audible for the driver due to wind and tire noises.

One of the vehicle parameters may also be an engine torque of a vehicleengine, which is provided, for example, by an engine control unit. Inthis case, the associated activation condition is satisfied, forexample, if the presently ascertained engine torque is lower than apredefined threshold value such as, for example, 80% of a maximum enginetorque. This activation condition is intended to ensure that sufficientpower reserves are available to be able to compensate for the brakingtorque by increasing the engine torque.

One of the vehicle parameters may also be a brake pressure, which may bemeasured, for example, with the aid of a pressure sensor. In this case,the associated activation condition is satisfied, for example, if themeasured brake pressure is equal to or lower than a predefined thresholdvalue such as, for example, 0 bar. This activation condition ensuresthat the rust removal function is not carried out during a brake pedaloperation. An operation of the service brake could optionally also bedetected using a brake pedal sensor such as, for example, a displacementsensor.

Another vehicle parameter may also be time information, which may bemeasured, for example, with the aid of a timer. The time information mayrelate to, for example, the operating time or the shutdown time of thevehicle. In this case, the associated activation condition is, forexample, satisfied if the measured time duration is greater than apredefined threshold value. The rust removal function may thus becarried out, for example, every 10 or 20 operating hours.

The brake pressure exerted by the rust removal function advantageouslyamounts to more than 5 bar and in particular more than 10 bar. The brakepressure during rust removal is preferably higher than in the case ofbrake disk wiping.

The duration of the rust removal is preferably individually adjustable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a brake system having a rust removal device according to anexemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a schematic diagram of a hydraulic brake system having twowheel brakes 13 and a rust removal device 10 for removing rust on wheelbrakes 13. Each wheel brake 13 includes a brake disk 12 and brake shoes11 and may be operated optionally using a foot brake pedal (not shown)and/or a brake actuator 5 such as, for example, a hydraulic pump.

In the case of electric and hybrid vehicles, wheel brakes 13 are usedrather rarely, since such vehicles are braked purely by a generator inmost cases. For that reason, rust may be deposited on brake disks 12,which reduces the braking power.

In order to improve the braking power, the depicted brake deviceincludes a rust removal device 10 having an algorithm stored in acontrol unit 1 and one or a plurality of sensors S₁-S_(n), which areconnected to control unit 1. The sensors measure various vehicleparameters such as, for example, the vehicle speed or a brake operatingstate, which will be explained in greater detail later.

Control unit 1 reads in individual sensor signals P₁-P_(N) and performsa rust removal function if sensor signal or sensor signals P₁-P_(N)satisfy a predefined activation condition. If the activation conditionis satisfied, brake actuator 5 is activated by control unit 1 via acontrol line 4 and automatically builds up a predefined brake pressureon wheel brakes 13, so that brake shoes 11 are applied to brake disks 12and they simply abrade away the rust. The brake pressure is maintainedfor a predefined period of time. Optionally, fewer or more sensorsS₁-S_(n) may also be provided, and accordingly fewer or more vehicleparameters may be monitored.

Sensor signals P₁-P_(N) read in from control unit 1 are, for example, anignition cycle counter content, a brake pressure such as, for example,the pre-pressure stipulated by the driver, an engine torque, anaccelerator pedal position, a wheel speed or vehicle speed, or a brakeoperating state which reveals whether the brake pedal is operated ornot. Corresponding sensors S₁-S_(n) are in this case an ignition cyclecounter, a brake pressure sensor, an accelerator pedal position sensor,wheel speed sensors and a brake pedal sensor such as, for example, apedal position sensor. The engine torque may be read in, for example,from an engine control unit 2.

In the present example, a rust removal function is performed if theignition cycle counter content is greater than the one in the mostrecently carried out rust removal, the vehicle speed exceeds apredefined threshold value of, for example, 30 km/hr or also 50 km/hr,the engine torque of the vehicle drive is lower than a predefinedthreshold value such as, for example, 80% of the maximum engine torque,and the vehicle is not momentarily being braked.

In the present exemplary embodiment, the rust removal function isactivated if all forenamed activation conditions are satisfied.Depending on the requirement, however, more or fewer activationconditions may also be defined.

The consequence of the automatic operation of brake shoes 11 for rustremoval is that the vehicle is decelerated slightly. In order tocompensate for this deceleration, it is provided here to increaseaccordingly the engine torque of a vehicle engine 3. To that end,control unit 1 generates a corresponding control signal which is sent toengine control unit 2 via a control line 6. The engine control unit thenincreases the engine torque of the vehicle engine such as, for example,an electric motor. As a result, the driver no longer notices adeceleration.

Using the rust removal device according to the present invention, therust is removed from brake disks 12 in regular intervals. As a result,it is possible to ensure a constantly good braking power of wheel brakes13.

What is claimed is:
 1. A device for removing rust from a brake disk of awheel brake, comprising: a control unit configured to automaticallyactivate a brake actuator in order to apply brake shoes to the brakedisk of the wheel brake if a first vehicle parameter satisfies a firstpredefined activation condition, wherein the first vehicle parameterincludes an ignition cycle counter content, and the first predefinedactivation condition is satisfied if an ascertained ignition cyclecounter content is greater than a predefined value.
 2. The device asrecited in claim 1, wherein the control unit also activates, if thefirst predefined activation condition is satisfied, a vehicle engine inorder to at least partially compensate for a braking action of the wheelbrake during rust removal.
 3. The device as recited in claim 2, whereina second vehicle parameter includes a vehicle speed, and a secondpredefined activation condition is satisfied if the vehicle speed ishigher than a predetermined threshold value.
 4. The device as recited inclaim 2, wherein a second vehicle parameter includes an engine torque ofthe vehicle engine, and a second predefined activation condition issatisfied if an ascertained engine torque is lower than a predefinedthreshold value.
 5. The device as recited in claim 2, wherein a secondvehicle parameter includes a brake pressure, and a second predefinedactivation condition is satisfied if a measured brake pressure is equalto or lower than a predetermined threshold value.
 6. A method forremoving rust from a brake disk of a wheel brake of a vehicle,comprising: automatically activating the wheel brake if a firstascertained vehicle parameter satisfies a first predefined activationcondition for activating the wheel brake in order to remove rust fromthe brake disk, wherein the first vehicle parameter is an ignition cyclecounter content, and the first predefined activation condition issatisfied if an ascertained ignition cycle counter content is greaterthan a predefined value.
 7. The method as recited in claim 6, furthercomprising: increasing an engine torque of a vehicle engine with the aidof a control unit in order to at least partially compensate for abraking effect of the wheel brake during rust removal.
 8. The method asrecited in claim 7, wherein a second vehicle parameter is a vehiclespeed, and a second predefined activation condition is satisfied if ameasured vehicle speed is higher than a predetermined threshold value.9. The method as recited in claim 7, wherein a second vehicle parameteris the engine torque of the vehicle engine, and a second predefinedactivation condition is satisfied if an ascertained engine torque islower than a predetermined threshold value.
 10. The method as recited inclaim 7, wherein a second vehicle parameter is a measured brakepressure, and a second predefined activation condition is satisfied ifthe measured brake pressure is equal to or lower than a predeterminedthreshold value.